The present invention relates to reservoir-mounted filter assemblies and particularly to filter assemblies mounted within two-piece reservoirs.
Fluid reservoirs are commonly constructed in sections and detachably secured together to form the reservoir. This construction technique permits the various sections of the reservoir to be made of sheet metal and press-formed into the various sections, which are then bolted or otherwise secured together to form the final reservoir. This usually has the advantage of being a cheaper construction, as well as permitting the reservoir to be disassembled for cleaning if necessary.
One problem with this technique is that the dimensional tolerances between the various portions of the tank are difficult to maintain. Such tolerances become a problem when it becomes necessary to mount elements of the system between any two portions of the tank.
For example, one preferred form of reservoir is constructed of upper and lower half shells. It has been found that it is desirable for a filter element to be mounted within the reservoir and that the base of the filter element be mounted below the fluid level within the reservoir to reduce aeration. With such two-piece reservoirs as just described the base of the filter assembly is necessarily mounted on the bottom of the reservoir and the cover and hold-down portion of the filter assembly is normally mounted within an access opening in the upper part of the reservoir. The access opening must be above the liquid level and thus is normally in the top portion of the tank.
It is generally necessary that certain minimum tolerances be maintained between the filter base and the cover member or hold-down member in order to assure that proper sealing occurs around the filter to insure that the fluid is properly filtered. Maintaining such tolerances is extremely difficult and normally requires considerable expense, especially for two-piece tank assemblies as described above.